In the context of this proposal, we will use pre-existing defined epitopes for Fransicella tularensis (FT), and using the core TRIAD vaccine design toolkit, define new epitopes for Burkholderia pseudomallei (BPM) and Burkholderia mallei (BM), the agents of meloidosis and glanders, respectively, for use in an epitope-based multipathogen prophylactic vaccine. FT has been listed as a Category A biological warfare agent as a result of World War II and Cold War-era biowarfare research. BPM, the etiological agent of melioidosis, is responsible for an estimated 20% of septicemias and approximately 40% of deaths due to bacterial sepsis in tropical regions of the world. BM, a related bacterium, also causes fatal infections (classified as glanders) in man and animals. Like FT, BM is highly infectious as an aerosol. All three pathogens (FT and BPM/BM) are intracellular bacteria and thus amenable to attack by cell-mediated immune response. The EpiMatrix epitope-based vaccine design platform has already yielded a prototype F. tularensis Type A (subsp. tularensis: SCHU S4) vaccine that confers 60% protection against heterologous lethal respiratory challenge with the live vaccine strain (LVS), an attenuated subsp. holarctica derivative. To our knowledge no subunit vaccine for tularemia has achieved a comparable level of protection in this well-developed lethal respiratory challenge model. This milestone was reached over the course of a 24 month funding period. The same vaccine design tools, made available in the context of this U19 program project, will facilitate the development a novel combined vaccine against the three pathogens. We will test the combined vaccine components, and optimize dose, delivery vehicle, and adjuvants, in a live challenge model. In addition to evaluating our epitope-driven vaccine, we will explore whether combining our FT/BPM/BM multi-pathogen vaccine with the anti-LPS vaccine developed by Dr. Steven Opal and colleagues will lead to improved protection against live challenge. The challenge studies will be carried out at NERCE in collaboration with Brown University (Steve Gregory, Steve Opal) investigators. This milestone-driven program will lead to proof-of-principle (evidence for protection against live challenge) and development of a licensable multi-pathogen biodefense vaccine within a five year time frame.